When forming a groove on a processing target film in a plasma etching process, it is known that bowing is generated, i.e., a sidewall of the groove is over-etched, rendering a space at a middle portion of the groove protruded. With the advance of miniaturization, due to this bowing problem, it becomes difficult to control a width of the groove as designed. As a resolution, described in Patent Document 1 is a technique of adding COS (carbonyl sulfide) to an etching gas.
Patent Document 1: Japanese Patent Laid-open Publication No. 2012-204668
Meanwhile when forming a groove on the processing target film in the etching process, if the sidewall of the groove is vertical, a reaction product (deposit) may be deposited on a bottom (corner portion) of the groove, thus affecting a performance of a device formed thereafter. By forming a slope (taper) of a certain inclination angle on the sidewall of the groove, it may be possible to remove the reaction product (deposit) readily, and in a subsequent process of depositing a film on the sidewall of the groove, the film may be easily formed. Conventionally, however, it has been difficult to form the taper while suppressing the bowing.
In the technique of Patent Document 1, although the bowing may be suppressed to some extent, it has been still difficult to form the taper on the sidewall of the groove.